Within the field of packaging of liquid products deaeration is a well established concept and deaeration is included as an essential step in most processing plants e.g. in plants where liquid product is received as a bulk in a first end of the line and delivered as individual packaging containers in the other end of the line. In the bulk product the amount of dissolved oxygen corresponds to the saturation concentration at that particular pressure and temperature. The total amount of oxygen may very well exceed this amount on due to previous processing of the product. For some product this amount of oxygen is acceptable, yet for others, and in particular fruit juices or products with an extended shelf-life the amount of dissolved oxygen has to be reduced further in order not to affect the product negatively.
To simplify the underlying theory, which obviously is well-established and well-known to the skilled person, the solubility of a gas such as oxygen or nitrogen in a liquid will depend of temperature and pressure. At lower temperatures more oxygen or nitrogen may be dissolved in the liquid than what is the case at a higher temperature, i.e. the saturation concentration is higher at a lower temperature. For pressure the relationship is reversed, the higher the pressure the higher the saturation concentration. This simple relationship establishes that in order to deaerate a liquid one or both of the temperature or the pressure may be altered. Also, it may be obvious that deaeration as such is not difficult to accomplish by simply dialing in the desired temperature and pressure of a particular saturation concentration in a vessel containing the liquid. In a commercial filling machine, however, the deaeration should allow treatment of thousands of liters of liquid product per hour with a requirement of being energy efficient which renders the theoretical approach of awaiting equilibrium to be reached inapplicable.
An established method for deaeration of a liquid is by a process called stripping. By mixing an inert gas, such as carbon dioxide or nitrogen into the liquid to be deaerated the equilibrium will be affected and other dissolved gases will diffuse into the gas phase inert gas. Bubbles will form and the mix will leave the liquid and may thereafter be vented off. This process is commonly performed in stripping columns, yet in U.S. Pat. No. 6,981,997 an inline solution is presented. In the disclosed embodiments carbon dioxide is injected and mixed into a pressurized and chilled stream of liquid to be deaerated. Following the injection of the inert gas the stream is guided by a pipe to a pressure reduction valve leading into another pipe, which pipe debouches into a vessel. In the vessel the carbon dioxide is vented off together with other gases which has diffused into the gas phase carbon dioxide, and the deaerated liquid is guided away from a bottom portion of the vessel by means of a third pipe.
A deaeration method more commonly used in the main field of the present invention is to make use of a vacuum deaeration in an expansion vessel connected to vacuum. A particular vacuum level corresponds to a particular boiling point of the liquid. The liquid is transported to the expansion vessel with a certain temperature which is some degrees above the boiling point which has been adjusted by way of the vacuum value. When the liquid enters the vessel the temperature falls immediately as the liquid boils or flashes and air (as well as other gases in the liquid) is expelled. The liquid vapors condense against cooled areas in the upper portion of the vessel, while the air which has boiled off is sucked away from the vessel by the vacuum pump. The deaerated liquid exits through an opening in the bottom of the vessel. In order to increase the separation rate the liquid may enter the expansion vessel in a tangential direction, so as to induce a swirl.
The above methods provide excellent deaeration of the liquid. Yet improvements resulting in improved energy efficiency and improved space efficiency are always contemplated. The present invention relates to such improvements.